In the examination of blood samples, it is often necessary or desirable to examine blood serum after it has been separated from the suspended cellular material, and for this purpose it is customary to subject the specimen tubes, in which the blood samples are delivered to the laboratory, to centrifuging action to cause the settling of the cells to the bottom of the specimen tube. Since many laboratories process large numbers of blood samples every day, facility of handling specimens and the ease of drawing off and retaining serum specimens are important to successful and safe operation.
The most widely employed method of separating the liquid phase component from the solid phase components of a blood mixture is centrifugation. When the serum is to be subjected to a diagnostic analysis with, for example, an automated electronic analyzer, it is important to employ a particulate-free specimen. Fibrin fibers are often the cause of analyzer malfunctions when they clog conduits or orifices in the analyzer.
Filtration has been employed previously to remove solid particles such as minute fibers of fibrin not readily separated by centrifugation. Illustrative of the prior art blood component filtration devices are those described in U.S. Pat. Nos. 3,481,477; 3,512,940; 3,693,804 and 3,832,141. In these serum separators, the sample is collected in a test tube and an elongated sampling tube is provided to fit within the test tube. In the lower end of the sampling tube is a piston head which makes a sliding seal with the side walls of the test tube. A filter is mounted in a passageway extending through the piston head to the interior of the sampling tube. As the sampling tube and piston head are pushed into the test tube, fluid will pass through the filter into the interior of the sampling tube leaving the residue in the bottom of the test tube. The sampling tube may subseguently be withdrawn at which time the filtrate which will be serum, will be withdrawn with the sampling tube.
Filtered serum may be withdrawn from the sampling tube for an automated blood analysis by using, for example, an aspirating tube. See, for example, U.S. Pat. No. 4,602,995. Alternatively, aliquots of serum may be transferred from the sampling tube into one or more sample containers by pipetting.
For automated laboratory analysis of blood samples, it is desirable to separate each sample into multiple pre-measured aliquots of serum. In this manner, a plurality of separate blood samples may be aliquoted and then all sample aliquots requiring a particular laboratory analysis may be run through an automatic analyzer sequentially.
There is a disadvantage associated with transferring serum from the sampling tube using pipetting or aspiration in that each of these techniques requires the introduction of a foreign object into the serum, sometimes more than once. For example, each introduction of a pipette or aspirating tube into serum sample involves the risk of contaminating the sample and also presents problems in maintaining the sterility of the pipette and/or aspirating tube.